MORGAN EDGE SETS HIS SIGHTS ON LENA - When multiple children get sick from lead poisoning, Morgan Edge (guest star Adrian Pasdar) points the finger at Lena (Katie McGrath) and blames her creation of the lead bomb she made to save National City from the Daxamites. While Lena knows she never intended any harm, she fears there may have been a flaw in her design, leaving her responsible. Kara (Melissa Benoist) teams up with Samantha (Odette Annable) to clear Lena's name, but it turns out to be harder than they thought. Meanwhile, Alex (Chyler Leigh) and Maggie (guest star Floriana Lima) make a crucial decision about the future of their relationship. Kevin Smith directed the episode

SUPERGIRL Episode Title: S03E06 "Midvale"

ESCAPE DOWN MEMORY LANE - Kara (Melissa Benoist) and Alex (Chyler Leigh) head home to Midvale for a little R&R. While there, Kara recalls a painful memory of a childhood friend's death and how that traumatic experience brought the Danver sisters closer together. Izabela Vidovic plays Young Kara and Olivia Nikkanen plays Young Alex in flashbacks

The Flash Episode Title: S04E05 "Girls Night Out"

KATEE SACKHOFF ("BATTLESTAR GALACTICA") AND EMILY BETT RICKARDS ("ARROW") GUEST STAR - Having received an ominous threat from her old boss, Amunet (guest star Katee Sackhoff), Caitlin (Danielle Panabaker) fears that her past time as Killer Frost may be back to haunt her. Felicity (guest star Emily Bett Rickards) comes to Central City to help the girls celebrate Iris's (Candice Patton) bachelorette party, while Cisco (Carlos Valdes), Joe (Jesse L. Martin) and the guys take Barry out for a night on the town.

THE FLASH Episode Title: S04E06 "When Harry Met Harry…"

ONE HARRY, TWO HARRYS, THREE HARRYS, FOUR - When collectors of Native American artifacts are attacked by a meta named Mina Chayton (guest star Chelsea Kurtz) who can bring inanimate objects to life, Barry (Grant Gustin) turns to a surprising ally for help. Determined to crack the identity of The Thinker, Harry (Tom Cavanagh) enlists Cisco's (Carlos Valdes) help to summon the ultimate think tank: "The Council of Wells'," a roundtable of the brightest Harrison Wells' from various Earths.

DC'S LEGENDS OF TOMORROW Episode Title: (#305) "Return of the Mack"

HELPING ONE OF THEIR OWN - When Nate (Nick Zano) thinks he has found a pattern to the anachronisms, it leads the Legends to London in 1897 to hunt down a time-traveling vampire. When they arrive in London, they run into Rip (guest star Arthur Darvill), but not everyone welcomes him back so quickly, leaving Sara (Caity Lotz) to make a tough choice in the end. Amaya (Maisie Richardson-Sellers) tries to connect with Zari (Tala Ashe), but she is still struggling with being part of the team. Meanwhile, Stein (Victor Garber) discovers what Ray (Brandon Routh) and Jax (Franz Drameh) are up to and is not entirely pleased.

DC'S LEGENDS OF TOMORROW Episode Title: S03E06 "Helen Hunt"

A DIFFERENT KIND OF WAR - When the Legends track down an anachronism in 1930s Hollywood, they discover it's none other than a time-displaced Helen of Troy and she's just started a war between two film studios. As the Legends try to fix history and return Helen (guest star Bar Paly) to the Bronze Age, things get complicated when they are blindsided by the appearance of a former enemy. Sara (Caity Lotz) contemplates an offer she is made, which would make the Legends leave the anachronisms be. Meanwhile, Stein (Victor Garber) and Jax (Franz Drameh) find themselves in an unusual predicament.

ARROW Episode Title: S06E05 "Deathstroke Returns"

Bennett) returns and asks Oliver (Stephen Amell) for help in tracking down his son. When they learn Joe (guest star William Franklyn-Miller) has been taken hostage by mercenaries, their mission to save him gets complicated by a terrible revelation that could shatter Slade's hopes of reunion forever. Meanwhile, Vigilante reappears in Star City. Joel Novoa directed the episode written by Ben Sokolowski & Spiro Skentzos (#605).

ARROW Episode Title: S06E06 "Promises Kept"

OLIVER MAKES A BIG DECISION - As Slade (guest star Manu Bennett) continues to uncover clues about his son's last few years, Oliver (Stephen Amell) makes a big decision. Meanwhile, the Green Arrow (David Ramsey) leads the team into battle against "The Dragon," a villain who is stealing valuable tech in Star City.